Liquid crystals have been used in the past in a wide variety of electro-optic and thermo-optic display applications. These include, in particular, electro-optic light modulating applications which require compact, energy-efficient, voltage-controlled light, such as watch and calculator displays. The electro-optic devices utilize the dielectric alignment effect in nematic, cholesteric and smectic phases of the liquid crystal, in which, by virtue of dielectric anisotropy, the average molecular long axis of the liquid crystal takes up a given orientation in an applied electric field. Thermo-optic devices accomplish the orientation or simple melting to the isotropic state via a temperature change.
The processes conventionally used for incorporating liquid crystals into a practical display form are generally complex and demanding. Display products are normally produced by sandwiching the liquid crystal material between two sheets of glass having electrically conductive coatings and then sealing the entire peripheral edge of the sandwich structure.
Conventional manufacturing makes it difficult to produce displays of large size, or having unusual shapes. In an attempt to expand the size and utility of liquid crystal displays, many methods have been suggested for coating liquid crystal material with various polymers to simplify their handling and generally allow for larger sheet construction of display or light modulating materials.
U.S. Pat. No. 4,435,047, for example, describes water emulsion methods both for encapsulating nematic liquid crystal material and for making a liquid crystal device using such encapsulated liquid crystal materials. However, there are a number of inherent difficulties one encounters when working with water emulsion systems. These include difficulty in obtaining and holding a uniform droplet size in the emulsion, poor spreading on plastic, and inability to dissolve and carry important additives in the system such as dyes, plasticizers, or electrical property modifiers.
More recently, a simplified approach was disclosed in "Field Controlled Light Scattering From Nematic Microdroplets", Doane et al. In this approach, microdroplets of a liquid crystal material were spontaneously formed in a solid epoxy polymer at the time of its polymerization. The cured polymer matrix containing these microdroplets was sandwiched between two layers of glass containing a conductive coating. This approach has simplified the manufacture of displays over processes using free liquid crystals or encapsulated liquid crystals. However, conventional curing of polymers such as an epoxy causes difficulties in coating and laminating in a continuous process. The materials are very low in viscosity during the coating step and cannot be laminated while soft due to leakage of monomer out of the edges of the laminate.
Light modulating materials containing microdroplets of liquid crystal material within a thermoplastic matrix have also been proposed. Such materials suffer a number of drawbacks in commercial application including limited temperature range, fatigue, slow switching times, and limited durability.